This invention relates to a tensionmeter for measuring the tension of an elongated object, such as a wire, tape, sheet or the like.
There is known a tensionmeter comprising three rollers arranged in the direction in which an elongated object to be measured (which will be referred to simply as an object) passes in successive contact with the rollers, the middle one of which is a sensing roller, so that the tension of the object may be measured by displacement of the sensing roller caused by the tension of the object. In this instrument, however, since tension is measured only by displacement of the sensing roller, measurement can not be conducted with high accuracy and precision. As the object passes the three rollers, it is bent into V-shape, so that a bending stress due to the inherent rigidity of the material of the object acts on the sensing roller as a displacing force, which causes errors in the result of the measurement.
To the best knowledge of the present inventors, there have been no tensionmeters in which the bending stress caused by the rigidity of the material of the object is taken into consideration.
One of the problems involved in the three-roller arrangement is the position or orientation of the detector including the three rollers. There will be no problem if the angle between the direction in which the sensing roller is displaced by the tension of the object under measurement and the direction of gravity is always a right angle. However, if the angle is not a right angle, the spring which resiliently supports the sensing roller receives not only the force caused by the tension of the object but also a component of the weight of the detector, so that errors are introduced into the result of the measurement. There are known no tensionmeters which are provided with means for eliminating the errors caused by the position of the detector.